Slags produced from electrosmelting of relatively low titanium bearing materials, essentially ilmenites, whereby iron is recovered are, in their own right, upgraded TiO.sub.2 materials generally suitable for production of TiO.sub.2 pigment by so-called sulfate process. However, the upgrading of ores through the electrosmelting process is made at the expense of iron and the ratio with respect to TiO.sub.2 to the other elements present in the ore such as Al, Si, Mg, Ca, Mn, V, Cr, etc. remain almost the same as in the starting ore.
In the chlorination of the slag, certain elements have essentially only an adverse economical impact due to a higher chlorine consumption per unit of TiO.sub.2 while some impurities cause technical problems (besides the economical aspect). The major source of trouble is due to the accumulation in the charge or feed of high-boiling point chlorides. These chlorides are in the liquid state during the fluidized chlorination reaction and are causing an agglomeration of particles resulting in poor chlorine utilization. Agglomeration finally leads to the defluidization of the bed. The alkali, alkali earth and manganese impurities in the feed are especially undesirable as impurities found in the feed.
While ilmenites rarely contain alkali compounds, many ilmenites contain significant amounts of MgO, CaO and MnO which are the major offenders affecting the reactions in the fluid bed during chlorination. The above mentioned oxides tend to concentrate in the slag during the iron recovery in the electrosmelting process, making the resulting titanous slag concentrate generally unsuitable for chlorination purpose regardless of the TiO.sub.2 grade.